Process of refining lead



Patented Aug. 11, 19 25 UNITED STATES PATENT OFFICE.

HENRY M, SCHLEICHER, 01E ROOSEVELT, AND HARVEY M. BURKEY, OF PLAINFIELD, NEW JERSEY, ASSIGNORS TO AMERICAN METAL COMPANY, LTD., OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

PROCESS OF REFINING LEAD.

No Drawing.

To all whom it may concern: F

Be it known that We, HENRY M. SC-I-ILEICH- ER and HARVEY M. BURKEY, of Roosevelt, Middlesex County, New Jersey, and 'Plainfield, Union County, New Jersey, respectively, have invented certain new and usefulv Improvements in Processes of Refinin Lead; and we do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process of separating arsenic and antimony and tin from lead and lead alloys such as lead bullion and antimonial or hard lead. The process is also capable of utilization in the removal of sulphur, selenium, tellurium and similar elements which are frequently present in crude lead.

The object of the invention is the provision of a method whereby arsenic and antimony and tin present in lead may be separately recovered. I

Another object of the invention is the provision of a method wherein the principal reagent employed is repeatedly returned for further use in the process so that the cost of operation is materially reduced, it being necessary only to supply additional quantities of the reagent to compensate for losses during the operation.

Further objects and advantages of the invention will be apparent as it is better understood byreference to the following specilication in which the preferred embodiment of the invention is described.

The use of an alkali metal compound in the separation of arsenic and antimony from crude lead has been heretofore suggested, the process involving the dropping of the molten lead through a molten bath of the alkali metal compound and the subsequent separation of the lead from the alkali metal compound. 'In this process, the separation is not readily accomplished and it is necessary to destroy a portion of the alkali metal compound which is retained and carried over by the molten lead from the bath. The process described does not accomplish the desired separation of the antimony and arsenic in an effective and satisfactory manner.

It has been discovered that the desired Application filed November 3, 1921. Serial No. 512,630.

separation may be accomplished by subjectmg the molten lead to an oxidizing condition preferably by blowing air through the molten lead in the presence of a material having an affinity for arsenic, antimony, tin and similar metals present in the lead which g are oxidized by the air passing therethrough.

Alkali metal compounds, and particularly sodium hydroxide in a molten condition, are suitable materials having the affinity referred to and these materials are preferably applied by maintaining a molten layer thereof upon the bath of molten lead. To prevent cooling the lead, the alkali metal compound is preferably melted before it is applied thereto and similarly the air may be preheated with advantage before it is introduced to the molten lead.

In carrying out the process, the lead is melted in a. suitable furnace or pot and the molten alkali metal compound is supplied thereto in sufficient quantity to provide a layer thereof upon the surface. The furnace is provided with tuyeres through which compressed air may be introduced beneath the surface of the'molten lead. These tuyeres preferably extend into and through the molten lead so that the air is thoroughly disseminated in the bath.

In the course of the process, arsenic, anti mony, tin and elements such as sulphur, selenium and tellurium are oxidized while the lead remains unaffected. The oxides, probably on account of their lower specific gravity, rise to the surface of the lead bath and immediately combine with the moltenalkali metal compound forming compounds of sodium and arsenic and compounds of sodium and antimony, for example; Thesearsenic and antimony compounds are absorbed by the excess molten alkali metal compound with the result that the molten layer stifi'ens perceptibly as the process proceeds. In the erable practice is to remove the layer of alkali metal compound when it contains in the neighborhood of 30% of arsenic and antimony. It has been determined that with this percentage the layer is still sufiiciently fluid to allow prills or small shot consisting of lead to settle therethrough. This lead shot is introduced into the molten layer of alkali metal compound by the bubbling of air through the lead bath, and so long as it may settle through the layer, the shot is not likely to be carried away when the bath is skimmed. Substantially no lead is combined with the alkali metal compound and any lead which is carried over in the form of shot is recovered and returned in accordance with the further procedure as hereinafter described.

The skimmings of' alkali metal compound carrying the antimony and arsenic are,while still warm or even hot, introduced into water and thus disintegrated to produce-a solution of alkali metal compound containing a relatively small amount of alkali antimony compounds and practically all of the alkali arsenic tin compotnids, and an insoluble residue consisting substantially of alkali antimony compounds. The residue is dried and treated in any desired manner and in accordance with practice well understood in the art for the recovery of antimony therefrom. The solution is treated to recover arsenic and tin. The solution is then evaporated preferably by the use of waste heat from a suitable source and the alkali metal compound is returned for further use in "treating fresh quantities of crude lead.

According to the preferred embodiment of the invention, the process may be carried out as follows:

The lead alloys such as antimonial'lead is melted in an iron or steel pot in a suitable furnace and is heated to a temperature of from 600 to 650 C. which temperature is preferably maintained during the further treatment of the lead. Sodium hydroxide or ordinary caustic soda is melted and a layer thereof amounting to 2 of the weight of the lead to be treated is applied to the surface of the lead bath. Air is then introduced to the lead bath through the tuycres as hereinbefore described, the operation continuing for approximately one hour or until the layer of caustic soda becomes thickened. to the desired point. The layer is then skimmed oil and a fresh layer of caustic .soda is supplied, the

blowin being resumed for a similar period. Tie alternate blowing and skimming is repeated as often as may be necessary to I remove the impurities. The skimmings will be found to contain approximately 30% of antimony, and by the operation described it is possible, for example, to remove 12% of antimony from a ton of antlmonial lead by subjecting it to twelve successive treatments with fifty pounds of caustic soda, each treatment requiring approximately one hour. The lead may thus be freed from antimony, the product being soft lead.

The skimmings are thrown into water as hereinbefore described with the resulting production of a strong caustic soda solution and an insoluble residue. The solution is decanted and the residue is dried and treated for the recovery of antimony or antimony compounds. This residue contains substantially60% of antimony mostly in pentavalent state, about 18% of sodium oxide and small amounts of iron. and

lead. .Before such treatment any lead shot melting furnace, and when concentrated and fused, the caustic soda is ready for re-use.

If the lead alloy contains arsenic and antimony, the greater part of the arsenic and tin is eliminated in the early part of theproeess, that is to say, in the first skimmings of caustic soda. Substantially all of the arsenic and tin are soluble so that they are almost completely separated from the antimony.

Any silver which may be present in the lead remains therewith, since it is unaffected by the process and does not enter the skimmings. The silver may be separated from the lead after the completion of the process in accordance with the usual practice.

From the foregoing it will be understood that the method herein described provides fdr the effective separation of other metals from lead and that the details of the operationare of such a simple character that they may be readily applied in an eeonomi cal manner to accomplish the desired object. Soft lead may be produced from lead containing considerable quantities of arsenic, tin and antimony at a minimum of expense and Without resorting to any expedients involving materials which are handled with difiiculty or which introduce losses in the process.

' Various changes may be made in the de tails of the process within the scope of the accompanying claims and without departing from the invention or sacrificing any of the advantages thereof.

We claim:

1. A method of removing antimony, arsenic, tin and similar metals from lead, which comprises subjecting the molten lead alloys at a temperature which materially senic, tin and similar metals from lead,

which comprises subjecting the molten lead alloys at a temperature exceeding 600 C. to a current of an oxidizing gas in the presence of a molten material having a selective aiiinity for the metals present in the lead, and separating the molten material with the antimony, arsenic, tin and similar metals from the lead. I

3. A method of removing antimony, ar-

senic, tin and similar metals from lead,

which comprises subjecting the molten lead alloys at a temperature between 600 and 650 C. to an oxidizing gas in the presence of a molten alkali metal compound, and separating the alkali metal compound with -the antimony, arsenic, tin and similar compounds, and precipitating arsenic com metals from the lead.

4. A method of removing antimony from lead, which comprises forcing-a current of air through the molten lead alloy at a temperature materially exceeding its melting point in the presence of an alkali metal hydroxide, and separating the alkali metal isorgpound containing antimony from the 5. A method of removing antimony from lead, which comprises forcin a current of- "lead, and leaching the alkali metal compound to recover the insoluble antimonyv compounds therefrom. 6. A method of removing arsenic from lead, which comprises forcing a current of a1r through the molten lead alloy in the presence of an alkali metal compound, separating the alkali metal compound from the lead, leaching the alkali metal compound, and precipitating the arsenic from the solutlon with a suitable reagent.

7. method of removing antimony and arsemc from lead, which comprises forcing a current of air through the molten lead alloy 1n the presence of an alkali metal compound, separating the alkali metal compound from the lead, leaching the alkali metal compound, 'withdrawing the insoluble antimony pounds from the solution with a suitable reagent.

8. A method of removing antimony, arsenic, tin and similar metals from lead, which comprises covering the molten lead alloy at a temperature which materially exceeds its melting point with a molten layer of an alkali metal compound, forcing air through the mass, and separating the alkali metal compound from the lead.

9. A method of removing antimony, arsenic, tin and similar metals from lead, which comprises covering the molten lead alloy with a molten layer of an alkali metal compound, forcing air through the mass,

skimming the alkali metal compound from the lead when the molten layer stiffens, and repeating the operation with fresh alkali metal compound until the impurities are substantially exhausted.

10. A method of removing tin from lead, which comprises forcing a current of air through the molten lead alloy in the presence of an alkali metalcompound, separating the alkali metal compound from the lead, leaching the alkali metal compound, and precipitating the tin from the solution with a suitable reagent.

11. A method of separating antimony, arsenic, tin and lead, which comprises forcing a current of air through the molten lead alloy in the presence of an alkali metal compound, separating the alkali metal compound from the lead, leaching the alkali metal compound, withdrawing the insolubleantimony compounds, precipitating the tin compounds from the solution by a suitable reagent and withdrawing the tin compounds from the solution.

12. A method of separating antimony, arsenic, tin and lead, which comprises forcing a current of air through the molten lead alloy in the presence of an alkali metal compound, separating the alkali metal compound from the lead, leaching the alkali metal compound, withdrawing the insoluble antimony compounds, precipitating the tin compounds from the solution by a suitable reagent, withdrawing the tin compounds from the solution, precipitating the arsenic from the solution and withdrawing the arsenic compounds from the solution.

In testimony whereof we affix our signatures.

MENRY M. SCHLEICHER. HARVEY M. BURKEY. 

